1. Field of the Invention
The invention relates generally to power systems for integrated circuits. More specifically, the invention relates to power conversion systems for low voltage, high current, integrated circuits.
2. Description of Related Art
As the power consumption of microprocessors and integrated circuits grow even beyond the 100 watt level, so too does the generated heat which must be dissipated. The traditional method of mounting the microprocessor on the motherboard and then applying upon it a heatsink and/or cooling fan will be inadequate for high level of power consumption. One solution for adequate heat dissipation is to mount the microprocessor on the back-chassis of a computer system since the back-chassis is usually composed of sheet-metal or other conductive material and is also exposed on the other side directly to the surrounding environment.
As the generated power of microprocessors grows to such high level, one must reduce the supply voltage to reduce the power dissipation. Power dissipation decreases quadratically with the supply voltage while the supply current decreases linearly with the supply voltage. The combined effect is that the supply current grows even though the power stays constant (due to reduced voltage). When a microprocessor is connected to the chassis, the chassis itself provides one of the high current terminals, but the other high current terminal must be connected to the microprocessor itself. Since the currents are high (on the order of 100s of amperes), the conductor has to be thick to reduce the voltage drop across the conductor and to reduce the noise due to inductance.
Prior art systems, as shown in FIG. 1, mounted a high voltage to low voltage converter 100 directly onto motherboard 120. A microprocessor 160 is mounted on a socket 125 of motherboard 120 and is attached to cooling devices such as a heat sink 140 and cooling fan 150. The converter 100 is located as close to the microprocessor 100 as possible to reduce the voltage drop over the large number of pins and conductors which must carry a large current. Converter 100 is connected to high voltage source and provides via connections 115 an output of low voltage, high current supply. When the microprocessor is mounted on the back chassis, the connection length and path from the top of the motherboard through the motherboard or around the motherboard increases the size and length of conductors required to supply the high current.
The typical voltage converter employed in microprocessor-based systems is a switching converter such as that shown in FIG. 2(a). A control signal 120 when asserted low will switch transistor T.sub.1 on and switch off transistor T.sub.2 allowing a large current to build up in inductor 130 which is coupled in series with transistor T.sub.1. Inductor 130 offers inertia for changes in its current and hence, will divert charge to capacitor 140, coupled at the output terminal 105, which builds a voltage across it. An oscillator and feedback system 150, coupled to capacitor 140 and transistor T.sub.1, compares a reference voltage (internally or externally supplied) with an output voltage 145 measured across capacitor 140. When the output voltage 145 is higher than the reference voltage, the oscillator and feedback system 150 will modify control signal 120 with shorter timing intervals so that T.sub.1 is switched on for a shorter duration, resulting in less current through inductor 130 and consequently, less output voltage. When output voltage 145 is less than the reference voltage, the oscillator and feedback system 150 will lengthen the timing interval of control signal 120 so that T.sub.1 is switched on for a longer duration, resulting in more current through inductor 130 and more output voltage.
FIG. 2(a) shows that power conversion is being performed for the benefit of a VLSI (Very Large Scale Integration) chip/load 170 that consumes the power from the output terminal 105. The voltage converter is external to load which it supplies. A first section of the switching converter 101 containing T.sub.2 and oscillator and feedback system 150 may be implemented using discrete components or as an integrated chip. Transistor T.sub.1 is typically implemented as a single component on the PC (printed circuit) board. Thus, the power transfer must occur through wires/connectors external to the load. Inductor 130 and capacitor 140 are also components mounted on the PC board or motherboard and are shown as block 103.
FIG. 2(b) shows a prior art switching voltage regulator 2000 which controls the power transferred to a load microprocessor/VLSI (or IC (Integrated Circuit)) chip 2700. Again, transistor T1, an inductor 2130 and a capacitor 2140 are mounted externally as is the voltage regulator. This voltage regulator has the control logic, previously described, and is typically implemented as a small analog integrated circuit. The FIGS. 2(a) and 2(b) systems are well-known in the prior art and have been implemented with a wide variety of components such as diodes and PMOS and NMOS transistors. When an external voltage converter is utilized, the output of the converter has to supply the high current to the microprocessor, or any such integrated circuit, that is mounted away from the voltage converter. To carry such high current over a long distance while limiting the voltage drop across the conductor, and while limiting the di/dt noise is very difficult. The difficulty arises in that a large current demands some combination of thicker conductors and/or a large number of supply pins to the IC or microprocessor. This also increases the area used up by the microprocessor and/or IC on the board or backplane.
To circumvent this problem, a power conversion system is needed which will allow a high voltage and low current source to be supplied to microprocessor or IC and then converted into a low voltage, high current source at/near the die of the microprocessor and/or IC where the high current is actually desired.
Thus, there is a need for a power conversion system that can be integrated efficiently into a microprocessor or IC such that a low current, high voltage source may be supplied to the microprocessor or IC thereby reducing the cost and complexity of the system in which the microprocessor or IC is employed.